Methods and devices for brain cooling for treatment and/or prevention of epileptic seizures

ABSTRACT

Passive prosthetic devices for focally cooling a brain and methods for inhibiting seizures are disclosed. The prosthetic devices replace a thermally insulating bone flap with a thermally conductive insert having an inner surface that contacts the relatively warm meninges or brain and an outer surface that contacts the relatively cool scalp. In an embodiment, the prosthesis is unitary; in another, a biocompatible casing is filled with a highly conductive core; in another, a filled polymer block is attached to a plate; and in another, the bone flap is filled with a conductive polymer. In one embodiment, a filled polymer containing elements that exhibit the magnetocaloric effect provide heat transfer that can be enhanced by application of a suitable magnetic field. Focal cooling as low as 1.2° C. has been found effective at inhibiting seizures.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/482,903, filed May 29, 2012, issued as U.S. Pat. No. 9,522,081, which claims the benefit of Provisional Application No. 61/491,139, filed May 27, 2011, and is a continuation-in-part of application Ser. No. 12/629,863, filed Dec. 2, 2009, issued as U.S. Pat. No. 8,591,562, which claims the benefit of Provisional Application No. 61/119,295, filed Dec. 2, 2008, the entire disclosures of which are each hereby incorporated by reference herein.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made with government support under NS053928 and NS042936 awarded by the National Institutes of Health and W81XWH-05-2-0072 awarded by the U.S. Army Medical Research and Materiel Command. The government has certain rights in the invention

BACKGROUND

Epilepsy is best understood as a syndrome involving episodic abnormal electrical activity in the brain, or epileptic seizures, that result from abnormal, excessive or hypersynchronous neuronal activity in the brain. It is estimated that 50 million people worldwide have epilepsy. The onset of epileptic symptoms occurs most frequently in infants and the elderly, and may also arise from trauma to the brain or as a consequence of brain surgery.

Epileptic symptoms are sometimes controllable with medication. However, nearly one-third (⅓) of persons with epilepsy cannot control seizures even with the best available medications. In certain cases, neurosurgery is undertaken to remove the epileptic focus to control the seizures.

For example, the high incidences of traumatic brain injury (TBI) in both the civilian and military populations, and the absence of any prophylactic treatment for acquired epilepsy, such as posttraumatic epilepsy (PTE), create an urgent need to develop broad-spectrum and easily deployable therapeutic strategies. There are currently no effective means for preventing the onset of PTE following head injury. The administration of anticonvulsants after head injury may decrease early posttraumatic seizures but has failed to impact the development of long-term epilepsy or improve the incidence of disability or death. Therefore, novel treatment paradigms are needed.

Several in vitro and in vivo studies have demonstrated that brain cooling by 10-20° C. reduces epileptiform activity in seizure models and in humans. Technologies based on cranially implanted Peltier (thermoelectric) cells powered by batteries have been considered to achieve such a high degree of cooling in the brain.

The process of epileptogenesis in humans is not known. It is theorized that agents that are neuroprotective may also be antiepileptogenic. Similarly, the process of ictogenesis (i.e., the precipitation of seizures) is not necessarily the same as epileptogenesis. It is therefore entirely possible that treatments that prevent the precipitation of seizures do not prevent the genesis of epilepsy and, vice versa, those that may prevent the onset of epilepsy may not be capable of shutting down existing seizures.

There are known devices that use active cooling to shut down epileptic seizures (antiepileptic effect). Known devices are based on the assumption that cooling a targeted area of the brain by about 10° C. is necessary to shut down the epileptic focus. One such device is based on active Peltier cells that cool the brain, including heat pipes to cool deep into the brain. A second exemplary known device uses circulating coolant in tubing implanted within the dorsal hippocampus of a brain to achieve cooling of at least 7° C. in the hippocampus. Unfortunately, such devices are typically highly intrusive (if inserted deep into the brain) and require the implantation of complex structures (e.g., heat pipes), electronics (Peltier elements), and long-lasting powering elements (e.g., batteries) to produce the necessary cooling. None of the known methods and devices provide continuous prevention of epilepsy (epileptogenesis) but only provide remedial action when a seizure begins so as to lessen the severity of the seizure.

What is desired, therefore, is an improved device for preventing and/or treating acquired epilepsy.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

A fully implantable cooling device for providing focal cooling to a brain is disclosed that includes a thermally conductive prosthesis sized and configured to be inserted into an aperture formed in a skull, and configured such that an inner surface of the prosthesis contacts the brain or meninges, and an outer surface contacts a corresponding portion of the scalp. The implanted device replaces a thermally insulating bone section with a thermally conductive prosthesis to cool the contacted portion of the brain.

In an embodiment, the prosthesis may be configured such that it does not penetrate the meninges, and may optionally further comprise subcutaneous and/or subcranial cooling strips. In an alternative embodiment, the prosthesis may include a heat pipe or other highly conductive probe that extends from the inner surface of the prosthesis into the brain adjacent an epileptic focus.

In an embodiment, the prosthesis comprises a biocompatible casing, for example titanium, stainless steel, or polymer, and a thermally conductive core, for example aluminum, copper, or stainless steel. In an alternative embodiment, the prosthesis is of unitary construction.

In an embodiment, the prosthesis comprises an inner portion, for example a block of a matrix material, for example silicone, containing a plurality of embedded thermally conductive elements, and an outer plate that engages the skull. Alternatively, the prosthesis may comprise a bone flap removed from the skull and modified to incorporate a thermally conductive matrix material extending through the bone flap, and contacting the brain or meninges and the scalp. The embedded thermally conductive elements may be diamond, graphene, gadolinium or other magnetocaloric material, carbon nanotubes, copper beads or the like.

A method for inhibiting epileptic seizures is disclosed comprising removing a portion of a skull to form a recess, and implanting a thermally conductive passive cooling device, for example a device in accordance with those described above, and having an inner surface that contacts the brain or meninges, and an outer surface that contacts the scalp, to cool the contacted portion of the brain.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a partial cross-sectional view of a representative brain-cooling device in accordance with the present invention;

FIGS. 2A-2C illustrate implantation of the brain-cooling device shown in FIG. 1;

FIG. 3 is a cross-sectional view of the brain-cooling device shown in FIG. 1, with a thermally conductive biocompatible cushion to enhance its heat gathering function;

FIG. 4 is a perspective view of a second embodiment of a brain-cooling device in accordance with the present invention having an outer plate fixed to a block-like insert;

FIG. 5 is a perspective sectional view of a third embodiment of a brain-cooling device in accordance with the present invention formed by modifying a bone flap to incorporate a conductive member extending through the bone flap;

FIG. 6 illustrates the brain-cooling device shown in FIG. 4 or FIG. 5 and using a filled polymer with elements that exhibit the magnetocaloric effect, and further including a device for generating a magnetic field that interacts with the magnetocaloric elements;

FIG. 7 illustrates various example cooling devices, in accordance with aspects of the present disclosure;

FIG. 8 illustrates an example cooling prosthesis, in accordance with various aspects of the present disclosure;

FIG. 9 is a partial cross-sectional view of a representative brain-cooling device as disclosed in some example embodiments herein;

FIG. 10 is a cross-sectional view of a typical craniectomy site wherein bone and scalp are removed to reveal the dura mater surrounding a brain;

FIG. 11 is a cross-sectional view of a portion of a brain-cooling device shown in FIG. 8 inserted into a craniectomy site;

FIG. 12 is a cross-sectional view of a brain-cooling device shown in FIG. 8 embedded within the cranium;

FIG. 13 is a cross-sectional view of the brain-cooling device of FIG. 11, showing the general heat-flow during operation of the brain-cooling device;

FIG. 14 is a second embodiment of a brain-cooling device in accordance with the present invention, having a conformal polymer layer adjacent the dura;

FIG. 15 is a third embodiment of a brain-cooling device in accordance with the present invention, having a thermally conductive biocompatible cushion adjacent the dura;

FIG. 16 is another example embodiment of a brain-cooling device in accordance with the present invention, having heat-collecting strips in contact with the dura; and

FIG. 17 is yet another example embodiment of a brain-cooling device in accordance with the present invention, comprising a heat-collecting insert without an external heat-dissipating plate.

DETAILED DESCRIPTION

Studies have suggested that cooling of the brain can assist in providing remedial effects to victims of epilepsy. Although a specific acquired epilepsy referred to herein as posttraumatic epilepsy (PTE) is relatively common, it will be appreciated that the provided embodiments are also effective in treating other types of epilepsy (e.g., reflex epilepsy, traumatic epilepsy resulting from stroke, epilepsy resulting from cerebrovascular disease, etc.). Prior art techniques have focused on a large degree of cooling (e.g., greater than 8° C.) and typically involve embedding active cooling devices deep within the brain (e.g., in the medial temporal lobe). Additionally, known methods focus on reducing the severity of a seizure after it has begun as opposed to preventing epileptogenesis using prophylactic measures, as provided herein.

The present inventors have developed a novel in vivo model of PTE in rats wherein chronic recurrent spontaneous partial seizures appear after a single event of a clinically relevant model of concussive closed head injury referred to as a fluid percussion injury (FPI). This model represents a significant departure from previous models of acquired epilepsy because the initiating insult, a transient compression of the meninges without penetration, is mechanically very similar to human cases of concussive closed head injury. In a recently completed blind, randomized preclinical study, the present inventors made the remarkable discovery that certain epileptic seizures can be prevented by very mild cooling of the surface of the injured brain in the region of the epileptic focus or injury. Positive results were found with focal cooling as low as just ˜1.2° C. These studies indicate that very mild focal cooling of portions of the neocortex, which may be maintained for a significant period of time, can reduce the risk of epileptic seizures in patients suffering from head injuries or the like. Unlike the relatively large degree of cooling suggested by the prior art, the mild cooling disclosed herein may be achieved using a passive cooling system.

In laboratory experiments, an implanted cooling device in accordance with the present invention have been found to significantly reduce the development of epileptic seizures. The implanted device produces a mild focal cooling of the neocortex (brain) through the meninges, for example, producing a localized cooling (ΔT) of less than 4° C. and even less than 2° C. The mild cooling indicated by the present invention can be accomplished with an extradural focal cooling device, i.e., without penetration of the meninges.

While passive heat transfer devices described herein are generally in contact with the meninges, it is contemplated that the device may alternatively be placed in contact with the brain itself. It will be appreciated, for example, that traumatic injuries to the central nervous system may rupture the meninges, and such a rupture site would be a potential area for use of the provided methods and devices. Thus, if the meninges are compromised, the provided embodiments can be used directly on the subdural central nervous system (e.g., neocortex of the brain).

As used herein, the cooling produced by the disclosed devices is defined to be the difference between the core temperature of the patient and the temperature measured at the interface of the patient and the inner surface of the cooling device.

Disclosed herein is a novel cooling device, specifically designed to perform cooling of the central nervous system, for neuroprotective, antiepileptogenic, and antiepileptic treatments. In the current embodiment, the cooling device is implanted in a recess sized and configured by removal of a portion of a patient's neurocranium or skull. As used herein, the terms “skull” and “cranium” are defined to mean the neurocranium or braincase, i.e., the portion of the skull that houses the brain. The embedded cooling device may be formed, for example, to fit in the location of a craniotomy or a decompressive craniectomy, and to achieve the desired degree of cooling. A heat-collecting internal surface of the device is placed in contact with the patient's meninges or brain. Optionally, flexible heat-conducting strips may be used to increase the heat transfer to the cooling device and/or to provide cooling to regions of the brain adjacent the site of the craniotomy.

After the desired cooling course of treatment, the cooling device may be removed and replaced by bone or plates, as per accepted current procedures. In some situations it may be preferable to leave the cooling device implanted permanently, or for an extended period of time, to allow for periodic cooling treatment.

The present invention provides methods for brain cooling to prevent epileptogenesis after brain injuries, methods for passive brain cooling to prevent ictogenesis and/or epileptogenesis, and devices for passive brain cooling.

A brain-cooling device in accordance with the teachings of the present invention will now be described further with reference to the FIGS., wherein like numbers indicate like parts. FIG. 1 shows a fully implanted passive focal brain-cooling device 100 in accordance with the present invention implanted in a patient. The focal brain-cooling device 100 is sized and configured to be inserted into a recess formed by removal of a portion of the patient's neurocranium 85, such that the device 100 contacts the meninges 95, preferably without significantly compressing the meninges 95. Although direct contact with the meninges 95 is currently preferred, it is contemplated that the device 100 may alternatively be placed in direct contact with the brain 80 (e.g., neocortex), for example, if an injury has ruptured the meninges 95.

The cranium 85 is a flat bone comprising a thick outer layer of compact tissue, a relatively thin and brittle inner layer of compact tissue, and an inner layer of cancellous tissue called the diploe. The cranium 85 is a good thermal insulator and therefore aids in maintaining the brain 80 at the relatively higher temperature, relative to the scalp. The human brain 80 typically maintains a temperature approximately equal to, or slightly greater than, the body core temperature. The scalp 90, by contrast, is typically several degrees cooler than the body's core temperature, although the scalp temperature will generally vary much more than the core temperature, and is more subject to environmental conditions. The human scalp is actively cooled though perspiration, and has among the highest density of eccrine sweat glands in the human body.

As noted in Specialized brain cooling in humans?, G. L. Brengelmann, The FASEB Journal Vol. 7, 1148-1153 (September 1993), “The few measurements of human brain temperature available support the concept that this large organ is at nearly uniform temperature, slightly above arterial temperature and not directly influenced by head surface temperature.” Although tympanic temperature falls when the face or neck are cooled, the tympanic temperature does not reflect brain temperature.

The focal brain-cooling device 100 is a thermally conductive device that replaces a small section of the thermally insulating cranium 85. The inner surface 102 of the device 100 contacts the relatively warm meninges 95 (or the brain 80) and the outer surface 104 contacts the relatively cool scalp 90. The device 100 therefore provides focal cooling to the region of the brain 80 adjacent the device 100 by increasing the heat transfer between the adjacent portion of the brain 80 and the scalp 90.

The focal brain-cooling device 100 in this embodiment includes a core 122 made of a highly thermally conductive material, and an outer casing 124 made of a thermally conductive biocompatible material. Representative core 122 materials include aluminum, copper, stainless steel, and other materials having high thermal mass and/or high thermal conductivity. The outer casing 124 may be a biocompatible metal, such as titanium, stainless steel, or a non-metallic biocompatible material known to those of skill in the art (e.g., biocompatible polymers). Alternatively the focal brain-cooling device 100 may conveniently be formed unitarily, for example, of stainless steel or titanium. A unitary construction requires both high thermal mass/conductivity and biocompatibility.

In a current embodiment, the inner surface 102 comprises a relatively soft and pliable material layer 103 having good thermal conductivity that is affixed to the outer casing 124. The inner layer 103 is conformable to optimize the contact between the inner surface 102 and the meninges 95. For example, the pliable layer 103 may be formed from a “soft” polymer such as a silicone (e.g., a polysiloxane).

The outer surface 104 of the outer casing 124 is substantially rigid and extends longitudinally beyond the aperture formed in the cranium 85 to define a protective rim or wings 126, such that the device 100 is precisely positioned with respect to the brain 80 and is prevented from being inadvertently inserted too far into the recess or inadvertently urged toward the brain, undesirably compressing the meninges 95 and/or brain 80.

FIG. 1 also shows optional heat-dissipating subcutaneous strips 128, which are formed from a thermally conductive, biocompatible material, and are fixed to the outer casing 124. The subcutaneous strips 128 increase the effective area of the outer surface 104 in contact with the relatively low temperature scalp 90, thereby improving heat transfer through the device 100.

Optional heat-collecting subcranial strips 130 are also fixed to the outer casing 124. The subcranial strips 130 are flexible, and may be similar in construction to the subcutaneous strips 128 discussed above, and/or may provide a mesh, webbing, or stripping extending out from the core 122 to cover a larger area of the meninges 95 to improve cooling efficiency. The subcranial strips 130 are sized and configured to be inserted beneath the cranium 85, adjacent the aperture formed in the cranium 85. The subcranial strips 130 may be extradural (i.e., disposed strictly between the cranium 85 and the meninges 95) or transdural (i.e., extending at least partially through the meninges 95). The subcranial strips 130 are good thermal conductors and are formed to be biocompatible.

In addition to increasing the net heat transfer through the device 100, the subcranial strips 130 may also be used to expand or shift the location of the focal cooling. In some situations, it may be desirably to provide focal cooling to a location on the brain 80 that is near or adjacent to the aperture formed in the cranium 85. For example, typically after removing a portion of the cranium 85, additional testing is conducted to more precisely identify the epileptic focus within the brain 80. If the epileptic focus is not directly beneath the cranial aperture, the subcranial strips 130 may be used to expand or shift the location of the cooling affect, without requiring any additional removal of cranial material. For example, the subcranial strips 130 allow the surgeon to more precisely locate the cooled region of the brain 80 to more closely correspond to the epileptic focus.

In another option, illustrated in FIG. 1, a small-diameter heat pipe 105 (shown in phantom) extends from the inner surface 102 into the patient's brain 80. The heat pipe 105 is sized and configured to extend to the epileptic focus. The heat pipe 105 (or more than one heat pipe) may be particularly useful in cases in which the epileptic focus is in a region of the brain that is not easily accessed, such as the ventral frontal or temporal lobe.

FIGS. 2A-2C illustrate steps for implanting the focal brain-cooling device 100, with the optional cooling strips 128 and 130 removed for clarity. FIG. 2A illustrates schematically a craniotomy site prepared for implanting the device, wherein a bone flap, i.e., a portion of the cranium 85, has been removed. Generally a surgeon or other medical practitioner will first identify a location on the brain 80 for which focal cooling is indicated. The precise location for bone removal and the desired angle of access may then be determined, for example, using various medical imaging technologies, for example, magnetic resonance imaging or the like. The patient's head is prepared for surgery, and the bone flap is removed to expose a selected portion of the meninges 95. In practice, the surgeon may at this time perform additional testing of the brain, for example, using deep brain stimulation or the like, to verify and/or adjust the optimal location for the cooling device 100, and to determined if subcutaneous strips 128 and/or subcranial strips 130 are indicated.

Referring to FIG. 2B, the cooling device 100 is inserted into the craniotomy site such that the inner layer 103 is adjacent the meninges 95, providing thermal communication between the brain 80 and the cooling device 100 through the meninges 95. If subcutaneous strips 128 and/or subcranial strips 130 are to be used, they would also be suitably positioned as indicated in FIG. 1. The cooling device 100 is inserted such that the protective wings 126 abut the cranium 85 to prevent undue pressure or displacement of the meninges 95 by the cooling device 100.

Referring to FIG. 2C, the scalp 90 is then closed over the cooling device 100 to fully implant the device 100. Heat is conducted by the device 100 from the relatively warm brain 80 (through the meninges 95) to the relatively cool scalp 90, as illustrated with arrows 98.

As shown in FIG. 3, the cooling device 100 may further include a thermally conductive biocompatible cushion 162 to enhance its heat gathering function. In this exemplary embodiment, the cushion 162 includes a silicone sack filled with a fluid (e.g., a saline fluid) and optional thermally conductive filaments 164 (e.g., steel wool). The cushion 162 provides a larger area of contact with the meninges 95 and readily conforms to the meninges 95. The composition of the cushion 162 allows for good thermal transport between the meninges 95 contacted by the cushion 162 and the cooling device 100.

Another embodiment of a passive focal brain-cooling device 200 in accordance with the present invention is shown in FIG. 4. In this embodiment, the focal brain-cooling device 200 comprises a relatively rigid plate 202, preferably formed from a high thermal conductivity material. Suitable materials include, for example, titanium, stainless steel, or a non-metallic biocompatible material such as biocompatible polymers. A biocompatible, thermally conductive block 204 is affixed to a lower face of the rigid plate 202. For example, the conductive block 204 may be formed from a soft, biocompatible polymer providing a matrix and having encapsulated therein thermally conductive elements. A polymeric matrix encapsulating thermally conductive elements is referred to herein as a “filled polymer.”

In a currently preferred embodiment, the filled polymer is a biocompatible silicone filled with highly conductive elements, for example, diamond, graphene, carbon nanotubes, copper beads, or the like. In particular, a filled silicone with graphene has been found to have very favorable thermal conductivity properties. Optionally, a pliable inner layer 203 may be used to contact the meninges 95 to improve heat transfer to the device 200.

Another embodiment of a passive focal brain-cooling device 210 in accordance with the present invention is shown in FIG. 5, with a portion of the device 210 cut away to show other features. In this embodiment the bone flap 212 (the portion of bone removed in a craniotomy) is retained and used to form the cooling device 210. The bone flap 212 is modified by drilling a plurality of holes through the bone flap 212. A highly thermally conductive component 214 is then formed, for example, by injecting and/or molding a biocompatible polymeric compound filled with high-conductivity elements (e.g., a filled polymer) into the plurality of holes. Preferably, the filled polymer will also be molded along at least a portion of the bottom surface of the bone flap 212 to conformably engage the meninges 95 for a good thermal connection. In other embodiments the polymer may be molded along at least a portion of the top surface of the bone flap 212 to conformably engage the scalp 90 for a good thermal connection. Suitable biocompatible filled polymers include a biocompatible silicone filled with highly conductive elements formed from diamond, graphene, carbon nanotubes, copper beads, or the like.

The devices 200, 210 may optionally utilize subcutaneous strips 128 and/or subcranial strips 130, as discussed above.

The filled polymer components 204, 214, discussed above, may be supplemented or alternatively filled with elements that exhibit the magnetocaloric effect. The magnetocaloric effect is a phenomenon wherein a reversible change in the specific heat of a material can be induced by subjecting the material to a changing magnetic field. For example, gadolinium demonstrates a magnetocaloric effect in which its temperature increases when it enters a magnetic field and decreases when it leaves the magnetic field. The magnetocaloric effect is stronger for the alloy Gd₅(Si₂Ge₂). It is believed that the use of filler elements exhibiting the magnetocaloric effect would allow the cooling effect of the devices to be controlled externally, i.e., by introducing a suitable magnetic field such that it interacts with the cooling devices.

For example, some persons experience warning signs prior to a seizure, such as odd feelings, unusual smells or tastes, confusion, a jerking movement of an extremity, tingling, and/or headaches. As illustrated in FIG. 6, at the first warning sign of a seizure a patient may activate an electromagnetic device 220 that is configured to engage or interact with the magnetocaloric properties of the cooling device 200, to induce the desired focal cooling to prevent or mitigate a seizure.

Any of the fully implanted devices disclosed in accordance with the present invention, e.g., cooling devices 100, 200, 210, may also give the patient the ability to effectively and rapidly provide focal cooling at the first sign of ictogenesis. For example, when a patient first detects a warning sign of the onset of a seizure, the patient may place an ice pack or other cold item against the patient's scalp, over the device 100, 200, or 210, thereby rapidly cooling the region of the neocortex adjacent the device.

FIG. 7 depicts various example embodiments of cooling devices, in accordance with the present disclosure. The embodiments in FIGS. 7A-70 are described hereafter. However, various combinations of the elements described in the example cooling devices depicted in FIGS. 1-16 may be employed in treating patients, in accordance with the present disclosure. FIG. 7A: Different patients with different kinds of decompressive craniectomies may benefit from customized plates of different shapes to be placed in different locations. FIG. 7B: Basic design of the passive cooling plate comprising a core of highly thermally conductive material (e.g., aluminum and/or copper) coated with biocompatible material such as titanium or steel. The heat-dissipating external plate is optional, depending on the extent of cooling desired. Note the temperature sensor at the bottom of the core, and the data transmitter/display on the external plate. FIG. 7C: Example of customization of the length and shape of the shaft crossing through the skin. FIG. 7D: Example of a cooling epidural strip that conveys heat from the surface of the dura mater to the core of the cooling device. FIG. 7E: Example of the cooling device with cooling strips connected to the core. FIG. 7F: cross-section of the patient's head showing reflected scalp, skull, and dura mater. FIG. 7G: placement of the core of the cooling device in the craniectomy. FIG. 7H: cooling device placed in the craniectomy with the scalp closed around it and with wound dressing in place. Once installed, the heat-dissipating external plate may be removed by the patient for cleaning and tending to the wound dressing. FIG. 7I: Schematics of the cooling device at work in its most basic configuration. Note the core absorbs the heat from the dura and conveys it to the heat dissipating plate. FIG. 7J: Schematics of the cooling device at work with cooling strips installed. Note the cooling strips absorb heat from a larger area of the brain relative to a simple core. FIG. 7K: Visualization of the cooling plate installed in the patient. If present, the heat-dissipating external plate protrudes from the head. It may be protected or, in cases where the external portion of the device is not attached to the implanted cooling device, the external portion may be held in place by customized hat or helmet. FIG. 7L: A thermally conductive biocompatible cushion is shown, which can be used to replace cooling epidural strips. The cushion may comprise a silicone bag containing saline and biocompatible “metal wool”. FIG. 7M: Schematics of the cooling device at work with thermally conductive cushion installed. FIG. 7N: Schematics of the cooling device at work with cooling strips installed, but no additional external heat dissipating plate. FIG. 7O: Schematics of the cooling device at work with cooling strips installed during brain edema, for which the decompressive craniectomy has been performed. Note the cooling strips allow for cooling even during edematous swelling of the brain.

In some examples, a cooling device in accordance with the present disclosure may optionally include a temperature sensor that is operationally connected to an external temperature monitor. FIG. 7B depicts one example embodiment where the external temperature monitor is mounted on the brain-cooling device, for example, on the heat-dissipating plate. The temperature sensor optionally includes communication means for transmitting the measured temperature to an off-patient monitoring system (e.g., a computer configured to monitor and log temperature) so as to allow for electronic access, manipulation, and monitoring (e.g., automated notification of doctors if certain temperature thresholds are breached) of the temperature measured by the device.

FIG. 8 illustrates another example cooling prosthesis. A) Schematics of a patient's craniectomy. These could be performed either as decompressive treatment after head injury, stroke, or other brain injuries, or in epilepsy patients suffering from pharmacoresistant seizures. Shape and dimension of craniectomies are customized to the patient's specific problem. B) Schematics of a coronal view of the craniectomy during surgery. C) The thermally conductive biocompatible mix of silicone and metal (steel or titanium) is cured into place to ensure good contact with the underlying dura mater. The curing process of silicone is biocompatible. D) While the conductive pad is curing, the rigid metal plate is put into position and anchored to the surrounding skull. The plate is made of titanium and has high mechanical rigidity to protect the underlying brain like the skull would. Note that both the rigid metal plate and the underlying pad may have a core of highly thermally conductive material, like aluminum or copper. The core of the plate is rigid, while the one for the pad is made of metal beads of various sides embedded in silicone. E) Principle by which the subdermal cooling device works. Because the scalp is at least 1.5-2° C. cooler than the brain, heat is dissipated from the brain, though the highly thermally conductive pad and plate, to the scalp. Note that the skull would prevent such head dissipation due to its very low thermal conductivity (table 1). F) Different implementation of the passive cooling device to include cooling strips and pipes. Strips (G) of highly thermally conductive material and biocompatible coating are placed under the scalp, and connected to the rigid plate, or under the skull and connected to the flexible pad. Pipes (H) are lowered through the dura and into the brain similar to electrodes for deep brain stimulation. The length and diameter is customized to the patient problem to achieve maximal heat dissipation in the deep structure of interest, while minimizing damage due to penetration. Strips and heat pipes increase the area of the brain affected by cooling. I) While the cooling device works without need for energy or batteries, placing an ice pack or other active cooling devices on the outside of the scalp can be used to increase the degree of cooling. These devices can be held in place by helmets. J) Different implementation of the cooling plate. Ridges to increase its heat exchange surface to the scalp are introduced.

The following description provides specific details for a thorough understanding of, and enabling description for, embodiments of the disclosure. However, one skilled in the art will understand that the disclosure may be practiced without these details. In other instances, well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the disclosure.

Disclosed herein is the discovery that that the dermal side of the scalp is naturally colder than the brain by ˜1.5-2° C. Thus, enhancing heat dissipation from the pathological brain to the intact scalp presents itself as a novel therapeutic modality to cool and treat the pathological brain. Accordingly, effective antiepileptic/antiepileptogenic treatments by cooling the perilesional cortex by ˜1.5° C. with a transdermal cooling piece has been achieved. In other embodiments, a cooling piece that is fully contained under the scalp and replaces an excised portion of the skull can be used. Such a subdermal cooling piece may eliminate the risk of infection in humans.

To implement this therapeutic modality, we use a cooling prosthesis and a type of flexible, soft and highly thermally conductive biocompatible material.

The prosthesis (FIG. 8) replaces a portion of the skull of the patient, and consists of two main components that are custom made to fit the patient's craniectomy, skull and dura mater thickness and shape, to achieve the desired extent and degree of cooling of the brain areas of interest. The heat-collecting plate is rigid, anchored to the surrounding skull, and provides the mechanical strength of the removed bone flap. This plate consists of a shell of biocompatible titanium, with a core of material with high thermal conductivity (aluminum/copper/graphite, etc.) to increase thermal conductivity while keeping the weight down (Table 1). The plate can be connected to an underlying soft pad placed in contact with the dura mater. The soft pad ensures efficient heat dissipation from the warmer brain to the colder scalp. In one embodiment, it can be made of highly thermally conductive material incorporating appropriate proportions of biocompatible silicone and micro-beads of various sizes of highly thermally conductive materials (Table 1). In this example, different proportions of silicone and micro beads can make the pad more or less flexible and thermally conductive, as desired. The pad may be composite with a core of different material and higher thermal conductivity.

TABLE 1 thermal conductivity and density of materials sorted by density. Thermal Conductivity Material [Btu/(hr ° F. ft)] Density (kg/m3) water 0.336 1000 silicone 0.5-1.7 1000-1300 Bovine cranial vault 0.335 1900 Graphite (||) 1126 2230 Graphite (⊥) 3.3 2230 Aluminum, pure 118 (at ~68° F.) 2640 Synthetic diamond 1350-1750 3220 Titanium 11-13 (at ~68° F.)  4500 Stainless steel 7-26 (at ~68° F.)  7850 Copper, pure 223 (at ~68° F.) 8930 Silver 235 (at ~68° F.) 10490 Gold 182 (at ~68° F.) 19320 Platinum  42 (at ~68° F.) 21400 ‘||’ indicates along the planes, and ‘⊥’ indicates perpendicular to the planes of hexagonal atomic lattice.

In further embodiments, therapy can be delivered actively by placing a cooling device on top of the scalp (FIG. 8 I), over the cooling plate. This device is placed externally, without a need for a burr hole though the scalp, through which to run wires, and which may increase the risk of infection. In one embodiment, the device is held in place by a helmet 815. In some embodiments, the device can be as simple as ice packs 811, or battery-powered peltier cells 813, etc., and it can be operated continuously, or intermittently (e.g., at night only), as desired to achieve maximum therapeutic effect with minimum disruption.

In further embodiments, therapy can be delivered actively by placing a cooling device on top of the scalp (FIG. 8 I), over the cooling plate. This device is placed externally, without a need for a burr hole though the scalp, through which to run wires, and which may increase the risk of infection. In one embodiment, the device is held in place by a helmet. In some embodiments, the device can be as simple as ice packs, or battery-powered peltier cells, etc., and it can be operated continuously, or intermittently (e.g., at night only), as desired to achieve maximum therapeutic effect with minimum disruption.

In one embodiment, attachments to the cooling device can be used to promote heat dissipation from surrounding brain regions (FIG. 8 F-H). Flexible sheets similar to ECoG strips can be connected to the rigid plate or the flexible pad to facilitate heat flux from the brain to the scalp. These strips (G) consist of a core of highly thermally conductive material, such as aluminum film, covered in biocompatible thermally conductive pad of silicone with metals or diamond micro-beads (Table 1). Similarly, heat pipes (H) of appropriate length and thickness can be lowered into the brain and connected with a flexible conductive material to the pad or plate (F). Both strips and pipes are used to convey heat from recessed brain areas of interest to the cooling plate. These strips and pipes can be especially useful in those cases in which the epileptic focus is in a brain area, such as the ventral frontal or temporal lobe, that is not easy to access and next to which a cooling plate cannot be placed. To improve heat dissipation toward the scalp, the rigid plate can be provided with ridges of 1-2 mm that increase its heat-exchange surface with the scalp (FIG. 8 J).

FIG. 9 shows a focal brain-cooling device 800 in accordance with the present invention, comprising a heat-dissipating plate 810 and a cooling insert 820. It will be appreciated that the brain-cooling device 800 need not be in two parts, but a separable device, such as that described herein, has advantages for the convenience of the patient when tending to the wound site created by the installation of the device 800. The heat-dissipating plate 810 in this embodiment includes a base 812 having a shaft 814 on one side including a threaded portion 816. A plurality of fins or ridges 818 are disposed on the opposite side of the base 812 to facilitate heat dissipation. The optional ridges 818 may be formed in other shapes known to those of skill in the art, and can be formed on both the top and bottom of the base 812.

The cooling insert 820 is sized and configured to be inserted into a recess formed by removal of a portion of the patient's cranium, such that the cooling insert 820 contacts the dura mater 1095 (see FIG. 11), preferably without compressing the dura mater 1095. Direct contact with the brain (e.g., neocortex) is also contemplated; particularly if an injury has ruptured the dura mater 1095.

The cooling insert 820 includes a core 822 comprised of a highly thermally conductive material, and an outer portion 824 comprising a thermally conductive biocompatible material. Representative core 822 materials include aluminum, copper, stainless steel, and other materials having high thermal mass and/or high thermal conductivity. The outer portion 824 may be a metal, such as titanium, stainless steel, or any other biocompatible material known to those of skill in the art (e.g., biocompatible polymers). It will be appreciated that the cooling insert 820 may conveniently be formed unitarily, for example of stainless steel or titanium, although such an embodiment is not illustrated herein. A unitary construction requires both high thermal mass/conductivity and biocompatibility. The outer portion 824, and in particular the bottom (“inner”) surface of the outer portion 824, is preferably in contact with the dura mater 1095 during use of the device 800 to thermally conduct heat away from the patient's neocortex.

The heat-dissipating plate 810 may be made of the same, or different, material as the cooling insert 820 (or core 822), so long as it facilitates passive heat transfer away from the brain. Subcutaneous dissipating strips (see FIG. 11) can be used in conjunction with, or instead of, the externally disposed heat-dissipating plate 810.

A pair of protective wings 826 extend laterally from an upper portion of the cooling insert 820 and position the cooling insert 820 at the desired location on the patient, additionally preventing the cooling insert 820 from compressing the dura mater 1095.

A cooling-insert socket 828 is adapted to receive the threaded portion 816 of the heat dissipating plate shaft 814. It will be appreciated that other means for connecting the heat-dissipating plate 810 to the cooling insert 820 are possible and contemplated by the present invention.

FIG. 10 illustrates schematically a craniectomy site wherein a portion of the cranium 1085 has been removed through an incision in the scalp 1090. The dura mater 1095 is revealed above the neocortex 1080.

Referring to FIG. 11, the cooling insert 820 is inserted into the craniectomy site such that the outer portion 824 is adjacent the dura mater 1095, providing thermal communication between the neocortex 1080 and the cooling insert 820 through the dura mater 1095. The protective wings 826 rest on the cranium 1085 to prevent pressure being exerted on the dura mater 1095 from the cooling insert 820.

Referring to FIG. 12, the scalp 1090 incision is closed over the cooling insert 820 and a wound dressing 1096 is applied to the site where the cooling insert socket 828 protrudes beyond the scalp 1090. The heat-dissipating plate 810 is illustrated in position to be attached to the cooling insert 820.

Referring to FIG. 13, the brain-cooling device 800 is assembled wherein the cooling insert 820 and the heat-dissipating plate 810 are in thermal, and mechanical, contact. Heat is conducted from the neocortex 1080, as illustrated with heat arrows 1098 through the dura mater 1095 to the cooling insert 820 and thence to the heat-dissipating plate 810, wherein the heat is convectively dissipated to the ambient air, as illustrated with heat arrows 1097.

A second embodiment of a brain-cooling device 850 is shown in FIG. 14, implanted in a patient. The brain-cooling device 850 is similar to the above-described device 800. In this embodiment, a thermally conductive conformable element such as a polymer layer 855 is provided on the cooling insert 820, sized and configured to provide conformal contact with the dura mater 1095. For example, the polymer layer 855 may be formed from a “soft” polymer such as a silicone (e.g., a polysiloxane). The soft nature of the polymer layer 855 allows for a more conformal contact with the dura mater 1095, to improve heat transport to the cooling insert 820.

Another embodiment of a brain-cooling device 860 is shown in FIG. 15. The brain-cooling device 860 is similar to the device 800 described above, and includes a heat-collecting element comprising a thermally-conductive biocompatible cushion 862. In this exemplary embodiment the cushion 862 includes a silicone sack filled with a fluid (e.g., a saline fluid) and optional thermally conductive filaments 864 (e.g., steel wool). The cushion 862 provides a larger area of contact with the dura mater 1095 and readily conforms to the dura mater 1095. The composition of the cushion 862 allows for good thermal transport between the dura mater 1095 contacted by the cushion 862 and the cooling insert 820.

Another embodiment of a brain-cooling device 870 in accordance with the present invention is shown in FIG. 16. In this embodiment a heat-collecting element is illustrated comprising cooling strips 875 that are directly linked to the core 822 and provide a mesh, webbing, or stripping extending out from the core 822 to cover a larger area of the dura 1095 than that covered by the core 822. The cooling strips 875 can be extra-dural or trans-dural (not illustrated). The cooling strips 875 have good thermal conductivity, and are also biocompatible. In one embodiment, the cooling strips are similar in composition to the core 822 and outer portion 824 of the cooling insert 820 (e.g., a metallic core surrounded by a biocompatible coating).

As previously described, in some examples the cooling device internal plate optionally includes a temperature sensor that is operationally connected to an external temperature monitor. In one embodiment, the external temperature monitor is mounted on the brain-cooling device, for example, on the heat-dissipating plate. The temperature sensor optionally includes communication means for transmitting the measured temperature to an off-patient monitoring system (e.g., a computer configured to monitor and log temperature) so as to allow for electronic access, manipulation, and monitoring (e.g., automated notification of doctors if certain temperature thresholds are breached) of the temperature measured by the device.

FIG. 17 illustrates another embodiment of a focal brain-cooling device 900 in accordance with the present invention, wherein no external dissipating plate is used. The scalp 1090 can therefore be fully closed over the implanted device 900. The brain-cooling device 900 may be substantially the same as the cooling insert 820 described above, but without the shaft 814 portion, wherein heat dissipation through the scalp 1090 provides the desired heat rejection to achieve the mild temperature reduction, e.g., 1.degree.-4.degree. C., as contemplated herein.

Optionally, high thermal conductivity subdermal cooling strips 864 may be provided, that are in thermal communication with the brain-cooling device 900, and extend laterally between the patient's scalp 1090 and cranium 1085. Additional elements, such as the polymer layer 855, cushion 862, or cooling strips 875, as described above, may also be used with the cooling device 900.

The cooling device shown in FIG. 17 may alternatively comprise an active cooling element (not illustrated), such as a thermoelectric cooler, as is known in the art, to achieve desired levels of cooling in the brain. The active cooling device may be advantageous, for example, to achieve higher cooling levels, for example focal brain cooling of up to 10.degree. C.

The present invention provides methods and devices for treating and/or preventing epilepsy. The inventors of the present invention discovered that focal cooling is both antiepileptic and antiepileptogenic. With the employment of seizures induced by a realistic injury, and in the absence of pro-convulsant drugs, it is found that cooling by as little as 1.2.degree. C. is sufficient to prevent and block seizures. The finding is notable because it is the first demonstration that minimal (e.g., <2.degree. C.) cooling can prevent or slow down epileptogenesis; and a disease-modifying effect was observed by passive focal cooling at room temperature.

This invention further encompasses novel prosthetic devices specifically designed to perform passive cooling of an injured central nervous system for neuroprotective, antiepileptogenic, and antiepileptic treatments. Passive brain cooling is not considered in known devices and methods because it has been assumed that therapeutic effects would only be achieved by significant cooling. The below-presented experimental data show otherwise.

The provided device can be removed and replaced by bone or plates, as per accepted current procedures, or left implanted chronically for continuous treatment.

In one aspect, a method for treating a patient suffering from a central nervous system injury is provided. In this aspect, the patient has not experienced epileptogenesis, and the method is performed as a prophylactic measure so as to prevent (and/or mitigate) acquired epilepsy and epileptogenesis.

In one embodiment, the method comprises focally cooling a portion of the patient's central nervous system to prevent secondary acquired dysfunction, wherein the cooling is accomplished by implanting a cooling device externally adjacent the dura mater overlying the portion of the central nervous system, wherein the portion of the central nervous system of the patient is cooled by the cooling device by not more than 10° C., and further wherein the cooling device is implanted prior to demonstration of central nervous system in the patient.

Any of the previously described devices (e.g., FIGS. 1-17) are compatible with the method. While passive cooling devices have been emphasized above, active cooling devices (e.g., thermoelectric coolers) are useful in this embodiment (e.g., FIG. 17) wherein an exclusively sub-dermal cooling implant can be used to focally cool the traumatized area of the brain to prevent epileptogenesis while saving the patient from the likely discomfort of having an externally-mounted heat-dissipating element 810. The present invention provides methods and devices for treating and/or preventing epilepsy. The inventors of the present invention discovered that focal cooling is both antiepileptic and antiepileptogenic. With the employment of seizures induced by a realistic injury, and in the absence of pro-convulsant drugs, it was found that very mild focal cooling of the brain, e.g., by not more than 4° C., and in some embodiments by as little as 1.2° C., is sometimes sufficient to prevent seizures. The finding is notable because it is the first demonstration that minimal (e.g., <2° C.) cooling can prevent or slow down epileptogenesis; and a disease-modifying effect was observed by passive focal cooling at room temperature.

This invention further encompasses novel prosthetic devices specifically designed to perform passive cooling of an injured central nervous system for neuroprotective, antiepileptogenic, and antiepileptic treatments. Passive brain cooling is not considered in known devices and methods because it has been assumed that therapeutic effects would only be achieved by significant cooling. The below-presented experimental data show otherwise.

The provided device can be removed and replaced by bone or plates, as per accepted current procedures, or left implanted chronically for continuous treatment.

It is also contemplated that the present invention may be employed in a method for treating a patient suffering from a central nervous system injury, wherein the patient has not experienced epileptogenesis, and the method is performed as a prophylactic measure so as to prevent (and/or mitigate) acquired epilepsy and epileptogenesis.

Particular details of experimental animal studies conducted by the present inventors using a novel in vivo model of PTE in rats employing a concussive closed head injury, referred to as a fluid percussion injury (FPI), are provided in the related U.S. Patent Publication No. 2010/0312318, which is hereby incorporated by reference. These details will not be reproduced here, for brevity. The results of the experiments indicate a robust antiepileptogenic effect of focal cooling at modest temperature decreases (e.g., less than 2° C.). Varying magnitudes of focal cooling were applied six days after FPI, and the effect on antiepileptogenesis was recorded. While 100% of animals without focal cooling went on to develop neocortical chronic recurrent spontaneous partial seizures (CRSPSs), only half of the animals focally cooled for three weeks at the injury site developed CRSPSs. In summary, it was determined that a prolonged 1-2° C. focal cooling of the injured neocortex over three weeks post-injury by a passive device is antiepileptogenic, prevents the onset of FPI-induced epilepsy that is resistant to valproate and carbamazepine, and yet is well tolerated by animals, as it does not affect core body temperature and does not induce pathology. Notably, cooling was initiated six days after head injury, and still demonstrated a potent antiepileptogenic effect.

In more recent experiments, the relationship between the cutaneous temperature of the temperature of the neocortex in rats with certain steps taken to more closely reflect physical aspects of human anatomy were studied. The animal skull was first provided with a 6 mm layer of acrylic to simulate the thickness and thermal insulation of a human skull. Four digital thermometers were used to monitor the core temperature (measured rectally), brain epidural temperature under the prosthesis, the scalp temperature, and the scalp cutaneous temperature. For experimental purposes, the cutaneous temperature was clamped using a temperature-controlled metal chamber that was placed in contact with the scalp. the neocortex was cooled with a copper plate prosthesis implanted within a craniotomy site, such that the copper plate was in contact with both the meninges and the overlying scalp. Therefore, while the modified skull effectively insulates the brain from a wide range of temperatures of the scalp, the prosthesis allows controlled focal cooling without affecting the body temperature.

The present invention is not limited to use with PTE sufferers, but can also be extended to other central nervous system injuries that would benefit from local mild cooling of the brain (e.g., stoke victims). The disclosed devices may be particularly beneficial to those suffering from pharmacoresistant neocortical epilepsy. The present invention may be applied as a prophylactic to provide prolonged minimal cooling of the injured brain or epileptic focus, without the undesirable side effects observed in previous clinical trials involving lowering core temperature after head injury or the technological challenges of safely achieving the at least 8-10° C. cooling previously assumed necessary for prevention of epilepsy.

While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. 

The invention claimed is:
 1. A brain cooling system, comprising: a passive thermal-transfer prosthesis sized and configured to replace a bone section in a skull, the prosthesis having an inner surface configured to contact a portion of a meninges or brain disposed in the skull, and an outer surface configured to contact a corresponding portion of a scalp covering the skull; and a thermally-conductive external component configured to overlay the corresponding portion of the scalp.
 2. The brain cooling system of claim 1, wherein the thermally-conductive external component comprises an ice pack.
 3. The brain cooling system of claim 1, wherein the thermally-conductive external component comprises at least one peltier cell effective to transfer heat from the corresponding portion of the scalp to an external surface of the thermally-conductive external component.
 4. The brain cooling system of claim 1, wherein the thermally-conductive external component comprises a base including a first side adjacent to the scalp and a plurality of ridges provided on a second side of the base opposite the first side.
 5. The brain cooling system of claim 1, wherein the thermally-conductive external component comprises a first surface effective to dissipate heat to ambient air surrounding the thermally-conductive external component and a second surface effective to conduct heat from the corresponding portion of the scalp.
 6. The brain cooling system of claim 1, wherein the prosthesis further comprises a heat pipe extending from the inner surface of the prosthesis.
 7. The brain cooling system of claim 1, wherein the prosthesis further comprises a heat pipe extending from the inner surface of the prosthesis through the dura and into a subcortical region of the brain.
 8. The brain cooling system of claim 1, wherein the prosthesis further comprises at least one thermally conductive subcranial strip that extends away from the inner surface of the prosthesis and is configured to be positioned adjacent the meninges.
 9. The brain cooling system of claim 1, further comprising a external head-mounted structure configured to hold the thermally-conductive external component over the corresponding portion of the scalp.
 10. The passive cooling system of claim 1, wherein the outer surface is a surface of an outer plate of the passive thermal-transfer prosthesis and the inner surface is a surface of an inner plate of the passive thermal-transfer prosthesis, wherein the passive thermal-transfer prosthesis further comprises an interior portion that is disposed between the inner plate and the outer plate, wherein the outer plate defines a flange that is configured to engage an outer surface of the skull.
 11. The passive cooling system of claim 10, wherein the interior portion comprises a biocompatible matrix material having thermally conductive elements embedded in the matrix material.
 12. A brain cooling system, comprising: a passive thermal-transfer prosthesis sized and configured to replace a bone section in a skull, the prosthesis having an inner surface configured to contact a portion of a meninges or brain disposed in the skull, and an outer surface configured to contact a corresponding portion of a scalp covering the skull; a temperature sensor configured to detect a temperature of the meninges or brain; and an external temperature monitor communicatively coupled to the temperature sensor, the external temperature monitor effective to provide an indication of the temperature detected by the temperature sensor.
 13. The brain cooling system of claim 12, further comprising: a computing device configured in communication with the external temperature monitor, the computing device effective to: store the indication of the temperature in a log; and compare the indication of the temperature to a threshold temperature.
 14. The brain cooling system of claim 13, wherein the computing device is further effective to: determine that the indication of the temperature exceeds the threshold temperature; and generate an alert.
 15. The brain cooling system of claim 12, wherein the passive thermal-transfer prosthesis comprises a biocompatible outer casing and a thermally conductive core.
 16. The brain cooling system of claim 15, wherein the biocompatible outer casing comprises one of titanium, stainless steel, and a biocompatible polymer.
 17. A method of cooling a brain in a skull, the method comprising: passively transferring heat from a portion of the brain to a corresponding portion of a scalp with a passive thermally-conductive prosthesis positioned in an aperture formed in the skull, the passive thermally-conductive prosthesis having an inner surface contacting a portion of a meninges or brain disposed in the skull, and an outer surface adjacent to the corresponding portion of the scalp; and transferring heat from the portion of the scalp with an external cooling component adjacent to an exterior surface of the corresponding portion of the scalp.
 18. The method of claim 17, further comprising periodically applying the external cooling component at a position that overlays the exterior surface of the corresponding portion of the scalp.
 19. The method of claim 17, wherein the external cooling component is activated periodically.
 20. The method of claim 17, wherein the transferring heat from the portion of the scalp comprises activating a peltier cell of the external cooling component.
 21. The method of claim 17, wherein the passive thermally-conductive prosthesis comprises a biocompatible matrix material having a plurality of thermally conductive elements encapsulated in the biocompatible matrix material.
 22. The method of claim 17, wherein the external cooling component is effective to passively transfer heat from the portion of the scalp to the exterior surface of the corresponding portion of the scalp. 